Technique for generating spherically contoured tools

ABSTRACT

Spherically contoured tools for use in crystallographic orientation angle connection of crystal plates and the like are formed by machining recesses at appropriate locations on two plates such as lapping plates. For example, a recess is machined around the outer periphery of the first plate and about the inner periphery of the second plate. The plates are then mounted in contact with the faces of contouring gears and subjected to lapping in a planetary lapping machine. A spherically convex contour is imparted to the first plate and a spherically concave contour is imparted to the second plate.

United States Patent 1191 Miller 1111 3,802,064 1451 4 Apr. 9, 1974TECHNIQUE FOR GENERATING SPHERICALLY CONTOURED TOOLS [75] Inventor:Anton Johann Miller, Allentown,

[22] Filed: Dec. 22, 1972 [21] Appl. No.: 317,514

3,364,629 1/1968 Zalewski 51/283 Primary Examiner-Charles W. LanhamAssistant EJtaminer-Victor A. DiPalma Attorney, Agent, or Firm-A. D.Hooper 5 7] ABSTRACT spherically contouredtools for use incrystallographic orientation angle connection of crystal plates and thelike are formed by machining recesses at appropriate locations on twoplates such as lapping plates. For example, a recess is machined aroundthe outer periphery of the first plate and about the inner periphery 'ofthe second plate. The plates are then mounted in contact with the facesof contouring gears and subjected to lapping in a planetary lappingmachine. A spherically convex contour is imparted to the first plate anda spherically concave contour is imparted to the second plate.

10 Claims, 5 Drawing Figures 52 us. c1.. 29/558, 51/283, 51/323 51 Int.Cl 823p 13/04 [58] Field of Search 29/558,557; 51/283, 284, Y 51/323[56] J References Cited UNITED STATES PATENTS 2,378,243 6/1945 Penberthy51/283 X 2,479,204 8/1949 Buchele 51/283 2,668,397 2/1954 Holzrichter etal...: 51/323 X TECHNIQUE FOR GENERATING SPI-IERICALLY CONTOURED TOOLSBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to the formation of spherical contours and more particularly toa method of producing spherically contoured tools for such uses ascorrecting the crystallographic orientation angle of crystal plates.

2. Description of the Prior Art Spherically contoured tools such asmounting apparatus, grinding or lapping plates, etc., are often requiredin such applications as contouring optical lenses and the like. Inapplicants copending application filed concurrently herewith a method ofcorrecting the orientation angle of crystals by forming mesas on themajor surfaces of the crystals and subsequently double face lapping thecrystals is described. One technique for forming the mesas by lapping orgrinding the crystal to remove a wedge of material therefrom while thecrystalwas held in a spherically deflected configuration was alsodescribed. This technique required either a spherically contouredmountingmeans or correction tool upon which the crystals were mounted inspherical deflection or a spherically contoured lapping or grindingtool. Further, in one described method of mounting the crystals to thespherically contoured correction tool, a spherically contoured pressureplate is utilized to obtain a uniform bonding layer. The desiredaccuracies in the described angle correction proocess require that thespherically contoured tools, etc., be very precise. The amount of anglecorrection provided thereby depends in part upon thedegree of contour ofthe correction tool. Accordingly it is desirable to beable to generate avariety of spherical contours for correction tools. I

At present, spherically contoured tools may be formed by machining in alathe or similar apparatus. However-tools formed by this procedure arerelatively expensive because of the machining time involved and theaccuracy thereof may not be as good as required. Further a new machinesetup or calibration procedure is required foreach different sphericalcontour desired. Other methods of forming spherical contours also existbut they, also have the foregoing disadvantages of high cost and lack offlexibility to provide a range of contours without requiringrecalibration of the apparatus being utilized.

Accordingly it is anobject of this invention to improve the methods ofgenerating spherically contoured tools so that a wide range of contourscan be provided by one basic generating apparatus arrangement.

Another object is to improve the methods of generating sphericallycontoured tools to provide more accurate tools. w

Still another object is to simplify the methods of gen- .eratingspherically contoured tools to reduce the time and costs required forgenerating such tools.

SUMMARY OF THE INVENTION The foregoing objects and others are achievedin accordance with the principles of the invention by utilizing astandard planetary. double face lapping machine. Recesses are machinedor otherwise formed at selected locations in two plates such as twolapping plates. For

example,.one plate can have a recess machined around the outer peripherythereof and the other plate can have a recess machined around the innerperiphery thereof. Contouring gears, normally utilized forreconditioning out-of-flatness lapping plates, are then placed betweenthe two plates in a lapping machine. These reconditioning gears rotateabout their own vertical center axis as driven by an inner and outerdriving gears which are part of a lapping machine. The force balancebetween the plates and the gears causes more material to be removed fromthe plates in the vicinity of the recesses. Accordingly the first plateis lapped into a spherically convex contour and the second plate islapped into a complementary spherically concave contour. The degree ofcontour can be: controlled by monitoring the lapping time so that a widerange of spherical contours can be obtained without varying the lappingprocedure. The type of contour obtained can be varied by changing thelocations of the recesses.

BRIEF DESCRIPTION OF THE DRAWING The invention will be more fullycomprehended from the following detailed description and accompanyingdrawing in which:

FIG. 1 is an exploded perspective view of a contouring gears mountedbetween two lapping plates;

FIG. 2 is a sectional view along line 2-2 of FIG. 1;

FIG. 3 is a sectional view similar to FIG. 2 after the plates have beenlapped by the co ntouringgears;

FIG. 4 is a sectional viewof a plate during a process of forming twounrelated contours on a surface thereof;

and t FIG. 5 is a sectional view of the apparatus of FIG. 4 after thecompletionof the forma tiion of two unrelated spherical contours on asurface of the plate.

DETAILED DESCRIPTION The technique of this inventionis based upon thefact that in a planetary double face lapping machine a state ofequilibrium exists between the forces exerted by the upper and lowerlapping plates of the machine upon .any item such as a crystal platebeing lapped between the upper andlower lapping plates. Accordingly ifone lapping plate has a small area of contact with the item .beinglapped than the corresponding portion of the other lapping plate, theforce per unit area presented lapping machinewill lose their desiredflat condition. Accordingly, special lapping plates commonly calledcontouring gears are utilized to recondition out-offlatness lappingplates to the desired flat condition. As shown in an explodedperspectiveview in FIG. 1, the contouring gears 10 are placed between upper andlower lapping plates 12 and 14, respectively, and lapped therewith inthe lapping machine to recondition surfaces 16 and 18,, respectively.Contouring gears 10 rotate about their own respective axes 10a and aredriven by inner and outer driving gears, not shown, which constitutepart of a standard lapping machine.

In accordance with this invention, recesses are machined in plates 12and 14 at strategic locations so that the subsequent lapping withcontouring gears generates spherical contours on surfaces 16 and 18rather than returning these surfaces to a flat condition. As shown moreclearly in the sectional view of FIG. 2, in

one embodiment a recess 20 is formed around the outer periphery ofsurface 16 of plate 12 and a recess 22 is formed around the innerperiphery of surface 18 of plate 14. Recesses 20 and 22 can be formed bymachining or other well known techniques.

These recesses 20 and 22 cause the forces per unit area in section 24 ofplate 12 to be greater than the corresponding forces per unit area insection '26 of plate 14 because section 24 has a smaller area of contactwith gears 10 but the total forces must be in equilibrium as previouslydiscussed. correspondingly, the force levels in section 30 of plate 14are greater than the corresponding force levels in section 28 of plate12. Accordingly, during the subsequent lapping process more material isremoved from sections 24 and 30 than from sections 26 and 28,respectively, by contouring gears 10. As indicated in the sectional viewof FIG. 3 in an exaggerated form, this results in surface 16 beinglapped into a spherically convex contour and surface 18 being lappedinto a spherically concave contour. Spherically concave contoured plate14 can be used as the correction tool in the angle correction processfor crystal 7 plates previously referenced and spherically convexcontoured plate 12 can be utilized as the presure plate in the sameprocess.

The widths 32 and 36 of recesses 20 and 22, respectively, determine theforce levels and consequently the rate at which the spherical contoursare formed. The progress of the contoured surfaces 16 and 18 can bechecked periodically using a spherometer and the lapping operation canbe terminated when the desired contour is reached. The shape of thecontour increases with lapping time until recesses 21 and 22 have beencompletely removed at which point the contoured shape stabilizes anddoes not change with further lapping. Consequently lapping time can beused as a very good control of the contour once the particular lappingspeeds, abrasive size, etc., have beenselected. If desired, the depths34 and 38 of recesses 20 and 22, respectively, can be predetermined,taking into account the other factors of lapping speed, abrasive size,etc., so that these recesses disappear at precisely the desired contour.Thus periodic monitoring of the contours can essentially be eliminated.Alternatively, a plurality of recesses can be positioned on surfaces 16and 18 to either aid or oppose each other in order to freeze orstabilize a particular spherical contour at some stage of same basicprocedure by merely controlling the lapping times and characteristics ofthe recesses. This flexibility is very important in providingspherically contoured tools for various applications.

In a second embodiment of the method of the invention, two entirelyunrelated contours can be formed on different portions of a surface of acorrection tool. Such a tool advantageously could be utilized, forexample, in the referenced angle correction process to increase theusable mounting surface of a correction tool for correcting all crystalplates mounted thereon by substantially identical amounts. In the firststep of this embodiment, a single spherical contour is formed on anentire surface of the tool or plate as discussed with respect to thecontour on surface 18 of tool or plate 14 in FIG. 3. Subsequently, aportion 44 of the surface 18 is reconditioned into a flat condition asshown in FIG. 4. This can be accomplished, for example, by lapping toolor plate 14 in a lapping or grinding machine by well known techniques.

After thev formation of flat portion 44, a recess 58 is formed aroundthe outer periphery of the flat portion 44 of plate 14 by techniquespreviously discussed. Plate 14 is thensubjected to further lapping in adouble face lapping machine by contouring gears 11 as shown in FIG. 4. Apressure plate 46 holds contouring gears 11 in contact with plate 14.Pressure plate 46 is provided with a recess 48 about its innerperiphery. The width 54 of recess 48 as compared with the width 56 ofpressure plate 46 is determined by the width 52 of flattened portion 44as compared with the total width 50 of tool 14. The width 52 offlattened portion 44 advantageously may equal approximately one-half ofwidth 50 so that the width 54 of recess 48 equals one-half of width 56.Because of the force balances between gears 11, plate 14 and pressureplate 46, more material is removed from the recessed edge of flatportion 44, i.e., from the outer periphery thereof, than from the innerperiphery. Accordingly, portion 44 is lapped into a spherical contour asshown in FIG. 5 which is unrelated to the contour on the remainingportion 45 of surface 18. Portions 44 and 45 can have the same ordifferent degrees of contours as desired;

Crystal plates to be corrected .can be-mounted on both contouredportions 44 and 45 and simultaneously corrected by a single flat lappingor grinding plate as discussed in applicants previously referencedcopending application.

Although the foregoing discussion has dealt primarily with thegeneration of spherically contoured tools for angle correction-ofcrystals, many other applications of the technique are readily apparent.Plates 12 and 14 can be replaced by optical blanks which can be lappedinto contoured optical lenses by the indicated procedures. Opticalblanks can also be mounted, or otherwise held in place on plates 12 and14, or contouring gears 10 and lapped into spherically contoured opticallenses.

Further, the technique is not limited to lapping but can be utilizedwith grinding and-polishing procedures also.

The technique utilizes standard apparatus available in many crystal andoptical device manufacturing shops. The technique is relatively simpleand the accuracies obtainable thereby are very good. The production ofspherically contoured tools by this technique is expected to be easierand more economical than by any other existing method.

While the invention has been described with reference to specificembodiments thereof, it is to be understood that various modificationsthereto might be made by those skilled in the art without departing fromits spirit and scope.

I claim:

1. A method of generating spherically contoured plates comprising thesteps of:

forming at least one recess in a first surface of a first one of saidplates, said recess being substantially symmetrical with respect to thecenter of said surface; placing lapping plates between said first plateand a second one of said plates so that siad first surface of said firstplate and a first surface of said second plate contact said lappingplates; and lapping said plates with said lapping plates in a doubleface lapping machine whereby said first surface of said first plate islapped into a first spherical contour and said first surface ofsaidsecond plate is lapped into a second spherical contour complementaryto said first contour.

2. The method of claim 1 wherein said recess is 25 formed about theouter periphery of said first surface whereby said first sphericalcontour comprises a spherical convex contour and said second sphericalcontour comprises a spherical concave contour.

3. The method of claim 1 wherein said recess is formed at the center ofsaid first surface whereby said first spherical contour comprises aspherical concave contour and said second spherical contour comprises aspherical convex contour.

4. The method of claim 1 wherein said said first and second platescomprise substantially' circular plates having substantially equal firstsurfaces and having openings though the centers thereof, said firstrecess is formed about the outer periphery of said first surface of saidfirst plate; and including the step of forming a recess about saidopening in said first surface of said second plate whereby said firstspherical contour corriprises a spherical convex contour and said secondspherical contour comprises a spherical concave contour.

forming a second recess around the periphery of said flat portion;

placing lapping plates in contact with said flat portion of said firstplate; and

lapping said flat portion with said lapping plates in a double facelapping machine so that said flat portion is lapped into a thirdspherical contour, whereby two unrelated spherical contours can beformed on different portions of said first surface of said first plate.

9. A method of forming spherical contours on first surfaces of first andsecond objects comprising the steps of: V v

forming a recess in said first surface of said first objec't;

placing lapping plates between said first and second objects in contactwith said first surfaces thereof;

lapping said first and second objects with said lapping plates to removeportions of said first surfaces thereof whereby said recess causes saidfirst surface of said first object to be lapped into 'a first sphericalcontour andsaid first surface of said second object to be lapped into asecond spherical contour complementary to said first spherical contour.r

10. A method for generating spherically contoured lapping platescomprising the steps of:

forming a first recess around the outer periphery of a first surface ofa first lapping plate;

forming a second recess about the center of a first surface of asecondlapping plate;

placing contouring gears between said first and second lapping plates incontact with said first surfaces thereof; and lapping said first andsecond plates with said gears whereby said first surfaces of said firstand second plates are spherically contoured because of said first andsecond recesses. i

y i a: a: a 1-

1. A method of generating spherically contoured plates comprising thesteps of: forming at least one recess in a first surface of a first oneof said plates, said recess being substantially symmetrical with respectto the center of said surface; placing lapping plates between said firstplate and a second one of said plates so that siad first surface of saidfirst plate and a first surface of said second plate contact saidlapping plates; and lapping said plates with said lapping plates in adouble face lapping machine whereby said first surface of said firstplate is lapped into a first spherical contour and said first surface ofsaid second plate is lapped into a second spherical contourcomplementary to said first contour.
 2. The method of claim 1 whereinsaid recess is formed about the outer periphery of said first surfacewhereby said first spherical contour comprises a spherical convexcontour and said second spherical contour comprises a spherical concavecontour.
 3. The method of claim 1 wherein said recess is formed at thecenter of said first surface whereby said first spherical contourcomprises a spherical concave contour and said sEcond spherical contourcomprises a spherical convex contour.
 4. The method of claim 1 whereinsaid said first and second plates comprise substantially circular plateshaving substantially equal first surfaces and having openings though thecenters thereof, said first recess is formed about the outer peripheryof said first surface of said first plate; and including the step offorming a recess about said opening in said first surface of said secondplate whereby said first spherical contour comprises a spherical convexcontour and said second spherical contour comprises a spherical concavecontour.
 5. The method of claim 4 further including the step ofmonitoring said contours of said first surface of said first and secondplates during said lapping step so that said lapping step can beterminated when said contours reach preselected values.
 6. The method ofclaim 4 wherein said recesses are dimensioned so that said contours havedesired values when said recesses have been removed by said lapping stepwhereby said contours are retained during any additional lapping.
 7. Themethod of claim 1 wherein said first and second plates comprise theupper and lower lapping plates of said machine and said lapping platescomprise contouring gears for resurfacing said lapping plates.
 8. Themethod of claim 1 further including the steps of: lapping said firstplate in a lapping machine to remove a portion of said first sphericalcontour thereon to replace said portion by a flat portion; forming asecond recess around the periphery of said flat portion; placing lappingplates in contact with said flat portion of said first plate; andlapping said flat portion with said lapping plates in a double facelapping machine so that said flat portion is lapped into a thirdspherical contour, whereby two unrelated spherical contours can beformed on different portions of said first surface of said first plate.9. A method of forming spherical contours on first surfaces of first andsecond objects comprising the steps of: forming a recess in said firstsurface of said first object; placing lapping plates between said firstand second objects in contact with said first surfaces thereof; lappingsaid first and second objects with said lapping plates to removeportions of said first surfaces thereof whereby said recess causes saidfirst surface of said first object to be lapped into a first sphericalcontour and said first surface of said second object to be lapped into asecond spherical contour complementary to said first spherical contour.10. A method for generating spherically contoured lapping platescomprising the steps of: forming a first recess around the outerperiphery of a first surface of a first lapping plate; forming a secondrecess about the center of a first surface of a second lapping plate;placing contouring gears between said first and second lapping plates incontact with said first surfaces thereof; and lapping said first andsecond plates with said gears whereby said first surfaces of said firstand second plates are spherically contoured because of said first andsecond recesses.